For the second time, Apple has pushed back delivery of new 27-inch iMac models to 3-4 weeks, signalling further wait times for customers who order the larger of the two new iMac models. The 21.5-inch models are still somewhat constrained, but continue to list 7-10 business day ship times. Apple had previously warned that 27-inch models would be in very short supply, but expected demand to ease after the holiday shopping period.

The latest iMac models, which feature an ultra-thin edge and other new features including Fusion Drive options, the latest processors and a lack of any optical drive, have been in high demand since their introduction back in late November. Apple has allegedly had great difficulty getting sufficient quantity of the larger model in particular manufactured, though it did fill some orders for both models in December.
The new manufacturing process used to bond the display to the chassis -- removing a two-millimeter gap between the LED and the glass protecting it, thus cutting down on reflectivity -- has apparently made the latest iMacs much harder to make, though the smaller size of iMac has been mostly able to meet demand. It was initially available in a 1-to-3 business day timeframe but is still available from retail and online outlets.
Both models have won consistent praise for their superior display, improved performance and the elegance of the Fusion Drive technology, which moves the OS and frequently-accessed files onto a 128GB SSD "partition" but stores most files on a conventional hard drive, providing both large amounts of storage (up to 3TB) while giving users the much faster feel of SSD performance. The 27-inch, however, is the only one of the two models that is able to have its RAM upgraded through a user-accessible service door. Apple had listed the 27-inch models as shipping in "January" during the holiday period to avoid disappointment, but it now seems likely that orders placed recently are unlikely to ship earlier than the beginning of next month.